The present invention relates to a vehicle seats, in particular vehicle seats incorporating an arrangement for fore and aft seat position adjustment incorporating a hydraulic actuator.
Vehicle seats are typically mounted to the vehicle floor by means of a pair of laterally spaced apart seat track assemblies which provide for fore and aft adjustment of the seat position longitudinally within the vehicle. The seat track assemblies comprise a pair of cooperating track members, typically upper and lower seat track members, which are slidingly engaged together such that they can slide longitudinally relative to each other. One of the seat track members attaches to the vehicle floor whilst the other is attached to the seat in order to slidingly mount the seat within the vehicle.
The fore and aft position of the seat may be manually adjusted by manually sliding the seat along the seat tracks with a locking mechanism associated with the either or both of the seat track assemblies to selectively lock the seat tracks and seat in the desired position. Alternatively, and increasingly, a powered arrangement may be provided in which an occupant activates a powered drive which drivingly moves the seat along the seat tracks.
To lock the seat in position, and/or to provide powered movement and adjustment of the seat position, hydraulic actuators have been proposed. These actuators comprise pistons which move within a cylinder displacing hydraulic fluid as the seat position is adjusted and the seat moves along the seat tracks. In the case of powered systems pressurised hydraulic fluid is supplied to the actuators to move the piston, whilst in manual systems the piston is moved within the cylinder displacing hydraulic fluid. By closing operating valves to prevent the flow of displaced hydraulic fluid the position of the piston and so of the seat can be fixed and locked.
An example of a manual seat adjustment arrangement incorporating a locking hydraulic cylinder is described in U.S. Pat. No. 5,743,591, whilst a hydraulically powered system incorporating a hydraulic actuator is described in U.S. Pat. No. 5,435,625.
Such hydraulic actuator arrangements offer smooth and almost infinitely variable adjustment and locking of the position of the seat. This can be contrasted with the incremental locking provided by conventional mechanical arrangements. Hydraulically powered arrangements also offer the prospect of extremely quiet, near silent, operation, without the noisy mechanical gearing. In spite of these, and other, advantages hydraulic actuators for seat adjustment have not been adopted for widespread automotive use.
In particular, a major problem with such hydraulic actuator arrangements is the size and resulting cost of the actuator that is required in a practical automotive system. Specifically to comply with automotive crash loading requirements the seat must provide sufficient structural strength and withstand high crash loading without failing or allowing excessive movement of the seat. With a hydraulic actuator providing the locking, extremely high pressures, for example in the region of 1700 bar, may be generated within the actuator under the applied crash loading. The actuator, and its structural mounting within the seat assembly, must be capable of withstanding these high generated pressures and crash loading forces. This increases the size of the actuator, the quality to which it must be made, and increases the costs. As a result, and in part due to this problem hydraulic systems have not been adopted for widespread commercial automotive use.
It is therefore desirable to provide improvements to automotive vehicle seat fore and aft adjustment arrangements incorporating a hydraulic actuator which addresses the above described problems and/or which offers improvements generally.